1. Field
The present disclosure relates generally to measuring structures and, in particular, to measuring edges of structures. Still more particularly, the present disclosure relates to a method and apparatus for measuring the edge of cylindrical structures using x-rays.
2. Background
Radiography uses x-rays to view unseen or hard-to-image objects. Radiography has both medical and industrial applications. With respect to industrial applications, x-rays are used to make measurements. In particular, the measurement made from x-rays may be used as one form of non-destructive testing. X-rays are used to inspect materials for inconsistencies using x-rays to penetrate various materials. X-rays also are used to test and grade welds on objects. These objects include, for example, pressurized piping, pressure vessels, high-capacity storage containers, pipes, structural welds, machine parts, metal plates, and/or other suitable objects.
One type of radiography is tangent radiography. For example, tangent radiography is commonly used to make measurements of pipe walls. These measurements may be used to identify pipe wall thinning. Further, tangent radiography also has been used to look for bond separation and check liner conditions. Tangent radiography is commonly used to detect fine detail in the edges of cylindrical or curved structures. Tangent radiography is used to check for gaps, fit up, corrosion, degradation, and/or other types of inconsistencies.
For example, currently available tangent radiography systems may be used to make measurements of large structures, such as those greater than two meters in diameter. This type of radiography, however, has limitations in usefulness as the structure increases in size to around 10 meters or more in diameter. The standoff distances and trade-off in resolution and sensitivity make a quantitative evaluation of some structures impractical.
As a result, this type of measurement is rarely applied to aircraft. With rockets and missile systems, this type of radiography may be used with limitations to the resolution and the size of features that can be measured or detected. With tangential radiography, the x-ray beam unsharpness decreases the resolution and the size of features that can be measured or detected.
One solution may involve moving the detector closer to the region of interest. With a cylinder, the detector may be moved to take into account the change in transmission length at the edge of the cylinder. However, limitations may be present on how close the detector can be placed with respect to the location containing a feature.
The energies used to obtain the desired results may add to the scattering and size of the radiation fields that occur for this type of measurement. As a result, extensive shielding or having operators located remotely from the testing site may be required. These types of limitations increase the expense and/or decrease the feasibility of performing tests using tangential radiography for structures, such as aircraft.
Therefore, it would be advantageous to have a method and apparatus that takes into account one or more of the issues discussed above, as well as possibly other issues.